Increasing the molecular weight of polyesters

Abstract

A process is disclosed for increasing the molecular weight of polyesters, polyester copolymers or polyester blends, which comprises heating a polyester blended with a tetracarboxylic acid dianhydride and a sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester to above the melting point (glass transition temperature) of the polyester.

What is claimed is: 
     
       1. A process for increasing the molecular weight of polyesters, polyester copolymers or polyester blends, which comprises heating a polyester blended with a tetracarboxylic acid dianhydride and a sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester to above the melting point (in the case of crystalline polyesters) or to above the glass transition temperature (in the case of amorphous polyesters) of the polyester. 
     
     
       2. A process according to claim 1, wherein the polyesters, polyester copolymers or polyester blends are polyester recyclates recovered from domestic waste, industrial waste or useful material collections, production waste or obligatory returnables. 
     
     
       3. A process according to claim 1, wherein the tetracarboxylic dianhydride has the formula ##STR15## wherein R is C 4  -C 20  alkanetetrayl or a radical of formulae (Va)-(Vj) ##STR16## wherein Q is --CH 2  --, --CH(CH 3 )--, --C(CH 3 ) 2  --, --C(CF 3 ) 2  --, --S--, --O--, --SO 2  --, --NHCO--, --CO-- or >P(O)(C 1  -C 20  alkyl), and wherein the aromatic rings in the formulae and (Va)-(Ve) are unsubstituted or substituted by one or more C 1  -C 6  alkyl groups, C 1  -C 6  alkoxy groups or halogen atoms. 
     
     
       4. A process according to claim 1, wherein the sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester corresponds to the formula: ##STR17## wherein R 1  is isopropyl, tert-butyl, cyclohexyl or cyclohexyl which is substituted by 1 to 3 C 1  -C 4  alkyl groups; R 2  is H, C 1  -C 4  alkyl, cyclohexyl or cyclohexyl which substituted by 1 to 3 C 1  -C 4  alkyl groups;   R 3  is C 1  -C 20  alkyl or substituted or unsubstituted phenyl or naphthyl;   R 4  is H, M 2+  /2, C 1  -C 20  alkyl or substituted or unsubstituted phenyl or naphthyl;   M 2+  is a divalent metal cation, and   n is 1 to 6.   
     
     
       5. A process according to claim 1, wherein the sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester is a compound of formula: ##STR18## 
     
     
       6. A process according to claim 1, which comprises using a metal salt of the sterically hindered hydroxyphenylalkylphosphonic acid ester in admixture with a polyethylene wax. 
     
     
       7. A process according to claim 1, which comprises using 0.01 part to 5 parts of the tetracarboxylic dianhydride and 0.01 part to 5 parts of the sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester per 100 parts of polyester. 
     
     
       8. A polyester comprising a tetracarboxylic dianhydride and a sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester. 
     
     
       9. A polyester recyclate comprising a tetracarboxylic dianhydride and a sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester. 
     
     
       10. A PET or PBT recyclate comprising a tetracarboxylic dianhydride and a sterically hindered hydroxyphenylalkylphosphonic acid ester or half-ester. 
     
     
       11. A polyester obtained by a process as claimed in claim 1.